1. Field
Aspects of the invention relate to processes for producing an airbag covering having a leather layer, particularly for use in a motor vehicle. Aspects of the invention also relate to partial weakening, formed in the leather layer, for the initiation of a tear and/or the propagation thereof along a previously defined path.
2. Discussion of Related Art
Airbag coverings used in a motor vehicle are normally located in the region of the instrument panel, in the steering wheel, in the doors and seats or the vehicle's roof lining and should have an appealing visual appearance while not obstructing or interfering substantially with the airbag's deployment in the event of actuation.
In the upscale executive and luxury motor vehicle classes, particular value is placed on the visual appearance of such airbag coverings. Attempts were made to produce airbag coverings that were not discernible by vehicle passengers and that were completely integrated into the surrounding areas particularly in the region of the instrument panel. Nevertheless, even in these cases, the continuously formed decor materials were intended to tear open along a previously defined line, thus ensuring that coverings and covering parts can lift off and allowing complete deployment of the airbag.
In the past, it had become established practice that such tear lines were sewn and subsequently an incision (using blades) was made on the rear. The disadvantage, however, was that, with the changes in temperature and varying intensities of irradiation acting on such airbag coverings, after some time had passed, the tear lines began to show through and thus the goal of making the airbag coverings permanently invisible within the decor material was not obtained.
Examples of visible airbag coverings may be found, for example, in DE 195 16 230 C2 in which the tear initiation and propagation region in the airbag covering is realized by a constriction of the material both in the region of the essentially dimensionally stable decor substrate and in the decor material disposed above the substrate.
Furthermore, EP 07 116 27 B1, for example, discloses a device and a process for introducing the incisions in the airbag covering by means of laser beams from the side facing away from the passenger of the vehicle. In this regard, a series of blind holes are aligned with each other so as to create tear lines in a layered composite. A laser beam, which is also intended to penetrate the uppermost layer of the decor material at least in part, would need such a high output, however, that it could likewise penetrate all the layers disposed thereunder. The energy input into the entire airbag covering was thus so high that it was not possible to prevent fusions at least of partial regions and ablations of material and as a result it was not possible to permanently guarantee the appearance of the airbag covering in the desired manner. In those cases where the laser did not also weaken the uppermost layer of the decor material, there was too great a force counteracting deployment of the airbag such that it was not possible to guarantee complete and unobstructed airbag deployment.
The difficulty of controlling and regulating such lasers is described by way of example in DE 196 36 429 C1.
The necessity for applying energy outputs that are as low as possible when introducing blind holes or through holes in decor materials is increased still further when using leather or leather-like materials. In this regard, due to the fact that leather is a natural material, it has local variations in properties and anisotropies, for example in respect of stretching behavior, material density and the like. Thus, depending on the grain of the leather, it must be ensured that a desired residual wall thickness of the leather material is also guaranteed in those regions in which the grain of the leather leads to particularly deep incisions from the visible side. This is regularly not guaranteed by the prior art with the desired reliability and safety.